The present invention relates to a satisfactory hydraulic pump used as a power source such as a power source of a power steering of automobiles.
As such a hydraulic pump, Japanese Unexamined (KOKAI) Patent Publication No. 7 (1995)-279871 discloses a hydraulic pump in which a hydraulic pump unit is encased between a pump body and a pump cover, a bearing bush is inserted into a bearing hole, the bearing hole passes through the pump body and is formed in the pump body, the bearing bush supports a drive shaft for driving the hydraulic pump unit and a seal chamber is formed at the end portion of the bearing hole.
At the inner circumference side of the cylindrical bearing bush inserted into the bearing hole of the pump body, one streak of an oil groove is spirally formed. The oil groove opens toward both end portions of the bearing bush. The hydraulic oil leaked in the hydraulic pump unit side is led to the seal chamber through the oil groove.
In such a conventional example, the hydraulic pump unit is driven by the drive shaft supported by the bearing bush. That is, a pulley is installed on the end portion of the drive shaft projecting from the pump body and the drive shaft is driven and rotated by a belt wound on the pulley and thereby the function of the hydraulic pump is performed.
At this time, when the hydraulic pump unit is driven, oil is leaked from the hydraulic pump unit. This leakage oil is led from the bearing hole into the inside of the oil groove of the bearing bush. The hydraulic oil flowing inside the oil groove of the bearing bush is led into the seal chamber with lubricating between the bearing bush and the drive shaft. The lubrication between the bearing bush and the drive shaft is performed in such a manner that a moderate supporting gap is formed between the bearing bush and the drive shaft, lubricating oil is supplied from the oil groove into the supporting gap, oil film is formed by the rotation of the drive shaft, the oil film supports the drive shaft and the direct contact of metals between the drive shaft and the bearing bush is prevented.
The hydraulic oil led from the oil groove into the inside of the seal chamber is sealed by a seal member encased in the seal chamber.
However, in the conventional example, the oil groove having a constant sectional area is formed at the inner circumference side of the bearing bush. Thus, when the quantity of the leakage oil in the hydraulic pump unit side increases, the flow speed of the hydraulic oil flowing inside the oil groove becomes faster, and the hydraulic oil having a faster flow speed is led into the seal chamber. When the hydraulic oil having the faster flow speed in the oil groove acts on the seal member in the seal chamber, if the hydraulic oil has the energy which exceeds the sealing ability of the seal member, it is apprehended that the hydraulic oil leaks to the outside.